1. Field of the Invention
The present invention relates generally to joint packing of the distinct radially acting bias type with bridging segments and more particularly to oil ring assemblies for internal combustion engine pistons utilizing radially acting coil and serpentine expander rings.
2. Description of the Prior Art
Conventional oil control ring assemblies for internal combustion engine pistons usually include a piston oil ring having one or more outer circumferential rails for sliding contact against the cylinder wall of the engine under considerable radial pressure to control the flow of oil along the cylinder wall as the piston reciprocates. The radial pressure is usually provided by an expander ring in an inner circumferential groove in the piston ring held in radial compression by the piston ring. Thus, the expander ring exerts a radial force against the piston ring to expand it against the cylinder wall.
Both the piston oil ring and expander are usually split to provide a gap in their circumference to accommodate expansion and contraction of the rings for assembly purposes and to compensate for uneven cylinder walls during operation. The expander ring spans the gap between adjacent opposite ends of the piston oil ring, and during expansion and contraction of the piston ring, the expander ring rubs against the end portions of the piston ring. Considerable wear results because the expander rings are usually made from a helically coiled spring, such as shown in Hesling U.S. Pat. No. 3,195,903, or are made in serpentine fashion as shown in Thomas et al U.S. Pat. No. 3,000,677. In both instances, edges of the expander ring are in rubbing contact with edges of the ends of the piston oil ring. Expansion and contraction of the rings results in fretting wear, mostly on the inner periphery of the piston oil ring. In extreme cases, however, the expander may wear so thin that it breaks resulting in loss of pressure between the ring and the cylinder wall and consequently a loss of oil pressure in the engine.
In addition, since the ring groove in the piston is usually wider than the thickness of the piston oil ring, the ends of the ring, which define the ring gap, tend to flutter in the ring groove since they are not supported at the gap. This also contributes to fretting wear between the ring and expander and also reduces the effectiveness of oil control by the assembly.
Accordingly, an object of the present invention generally is to provide an improved oil ring assembly for internal combustion engine pistons and more particularly to provide means for reducing wear of the piston oil ring normally caused by the expander ring, especially reducing wear of the end portions of the piston oil ring and reducing flutter of the end portions.